The present invention relates to a microstructure composed of a microphase-separated block copolymer, and a process for producing the same. The present invention also relates to a pattern medium carrying a regular pattern corresponding to the microphase-separated structure, and a process for producing the same.
Recently, necessity for arranging fine, regular patterns, several to several hundreds nanometers in size, on substrates has been growing as electronic devices, energy storing devices, sensors and so forth are becoming more compact and functional. Therefore, development of processes which can produce these fine pattern structures at high precision and low cost has been demanded.
These processes for producing the fine patterns are generally based on a top-down procedure, represented by lithography, in which a bulk material is finely inscribed to have a shape. Photolithography used for finely processing semiconductors for production of LSIs is one of the representative examples.
However, the top-down procedure has increasingly become difficult to apply, viewed both from production equipment and process, as demands increase for finer patterns. In particular, production of patterns becoming finer to a size of several tens nanometer, needs a huge equipment investment cost, because it should be aided by electron beams or deep UV ray. Moreover, when fine patterning using a mask becomes difficult, there is no other way but to use a direct drawing procedure should be applied, which cannot avoid problems resulting from greatly decreased process throughputs.
Under these situations, processes based on a phenomenon in which a substance spontaneously forms a structure, the so-called self-assembling phenomenon, have been attracting attention. In particular, a process based on a self-assembling phenomenon of block copolymers, the so-called microphase separation phenomenon, is an excellent process in that it can give fine, regular structures of various shapes having a size of several tens to several hundreds nanometers by a simple coating procedure.
In other words, when dissimilar polymer blocks which constitute a block copolymer are nonmiscible with each other, they undergo microphase separation to self-assemble a microstructure of specific regularity.
The microphase separation of block copolymer produces a microstructure in which spherical or cylindrical microdomains are regularly arranged in a continuous phase, or in which lamellar microdomains are regularly arranged.
When a microphase-separated microstructure is used as an etching mask, it preferably contains cylindrical microdomains regularly arranged in a continuous phase while upstanding on a substrate (or being oriented in the film thickness direction).
Because, a structure with cylindrical microdomains upstanding on a substrate can be more freely adjustable for an aspect ratio (ratio of size of the domain extending in the direction perpendicular to the substrate surface to that extending in the direction parallel to the substrate) than a structure with spherical microdomains regularly arranged on the substrate surface.
When a microphase-separated structure containing spherical microdomains is used as an etching mask, on the other hand, the structure has an aspect ratio of 1 at the largest, which is smaller than that for a cylindrical domain structure upstanding on the substrate and has substantially no adjusting freedom.
The first example of conventional technique for producing microstructures with cylindrical microdomains upstanding on a substrate by utilizing microphase separation phenomenon of block copolymers include one in which a silane coupling film applied beforehand on a Si substrate is irradiated with soft X-ray to form a regular structure by utilizing the difference in wettability (interfacial tension) of two blocks constituting a block copolymer to the radiated part and non-radiated part (for example, see Non-patent Document 1).
The second example of conventional technique utilizes a phenomenon in which wettability (interfacial tension) of two blocks constituting a block copolymer changes depending on thickness of an organic layer formed on a substrate. This technique sets thickness of the organic layer on a substrate in such a way that these blocks have the same interfacial tension (neutral condition), and induces microphase separation on the surface to realize a fine, regular structure (for example, see Non-patent Document 2).
The third example of conventional techniques is one in which a thin film formed on a substrate surface is irradiated with a diffraction pattern of extreme ultraviolet (EUV) ray to modify the affected segment of the thin film (for example, see Non-patent Document 3).
Non-patent Document 1: Langmuir 2000, 16, 4625-4631
Non-patent Document 2: SCIENCE, VOL. 308, 8, Apr., 2005
Non-patent Document 3: NATURE, VOL. 424, 24, Jul., 2003
The regular structure provided by Conventional Technique 1 has a limited fineness of arranged regular pattern, because it depends on focusing extent of soft X-ray.
The regular structure provided by the second example of conventional technique has a limited combination of a polymer material which gives a fine, regular structure and organic layer on a substrate surface, and involves high difficulties coming from necessity for uniformly forming the layer of given thickness on the substrate.
The third example of conventional technique 3 needs a large-scale system for irradiating a substrate with a diffraction pattern of extreme ultraviolet (EUV) ray, and is considered to be very low in mass production capability.
It should be noted that wettability of a block copolymer layer with a substrate surface depends on temperature, with the result that temperature set for forming a regular, microphase-separated structure is an important parameter. The above-described conventional techniques, however, give no consideration to problems associated with the temperature dependence.